Alloy, electron emitter, and method of making same



Patented Oct. 9, 1934 UNITED STATES ALLOY, ELECTRON EMITTER, AND METHOD OF MAKING SAME Donald W. Randolph, Flint, Mich" assignor, by

mesne assignments, to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application May 6, 1932, Serial No. 609,773

15 Claims.

This case is a continuation, in part, of my prior application Serial No. 520,703, filed March 6, 1931, which in turn was a continuation in part of my prior application Serial No. 351,835, filed April 1, 1929.

This invention has to do with an alloy characterized by high resistance to corrosion and high electron emissivity, with electron emitters made of such alloy, and with the method of manufacture thereof.

The alloy is composed of a base metal, such as nickel, or cobalt, an electron emitting material of the alkaline earth group, preferably'barium, and the element chromium which serves not only to increase the emission of the alloy but also to retard the evaporation of the alloy.

The preferred composition of my alloy is as follows:

Chromium .5 to 10% Barium .01 to 80% Balance nickel.

In addition, I have found it desirable as an aid in metallurgical processing such as rolling, drawing, etc., to use up to 2% manganese, although this may be omitted if preferred. I have also found it convenient to follow customary metallurgical procedure, adding approximately .1%

magnesium to deoxidize the alloy, and increase its ductility. of this there remains but a trace in the final product.

The chief difficulty in the making of this alloy is that of obtaining the desired barium content. In the case of the lower barium contents, the alloy may be simply prepared by wrapping the barium in nickel foil, inclosing it in a practically air tight container, or otherwise preparing it to exclude moisture and prevent oxidation, and immersing it in the melt. The melt is maintained at a temperature somewhat above that of fusion, and after allowing just sufficient time for the barium to permeate the mass, it is poured into ingot form and drawn to the desired shape.

I have consistently obtained alloys containing as high as .17% barium by employing the process described and claimed in my copending application Serial No. 520,704, filed March 6, 1931. On occasion I have secured barium contents as high as 20% by this method.

I have obtained the maximum barium content by employing the following method: The desired amount of barium metal was suspended by means of a nickel wire at the center of a substantially spherical cold steel mold. The molten nickel- 65 chromium alloy was then poured into the mold completely inclosing the barium. By this means I obtained an alloy characterized by the fact that the concentration of barium was highest at the center of the mold. The alloy was, therefore, non-homogeneous, although at points an equal distance from the center of the mold, the alloy was homogeneous. At the very center of the mold there remains some free barium. Tests of the alloy indicated that the maximum barium content was .80%. It is my belief that this represents the maximum solubility of barium in a nickelchromium alloy.

Another method of obtaining high barium content is that disclosed in the copending application of Prof. Maurice deKay Thompson, Serial No. 569,265, filed October 16, 1931, which consists in inclosing the metals in a bomb and subjecting it to high temperatures so that the barium is vaporized, and in that form unites with the other metals.

The lower chromium limit is not an absolute one but is simply the least amount at which sufficient increase in emission has been obtained to make the alloy useful in present day vacuum tubes of low power. Using less than this amount simply reduces the effect of the chromium addition.

I have made up alloys containing percentages ofchromium approaching the limit of workability which is commonly held to be around 35% in nickel-chromium alloys. With these high chromium alloys I have found the rate of evaporation in vacuum to be so high as to render them undesirable for use in present day tubes. Work in this field has indicated that if more than about 10% chromium is used no increased emission is obtained. Hence 10% has been selected as the preferred upper limit of chromium content.

My preferred composition is susceptible of considerable variation. The use of the other alkaline earths, calcium and strontium is indicated, although it has been my experience that their rates of emission are so much lower that barium is much to be preferred.

I have substituted cobalt either wholly or partly for nickel, but have obtained inferior results both with respect to emission and resistance to corrosion.

It is obvious that manganese and magnesium may be replaced by any other materials having a deoxidizing function, or imparting the desired physical properties to the alloy.

In some cases it may be desirable to use a small percentage of silicon as a help in alloying, rolling, or drawing- In my copending application Serial No. 609,771

filed May 6, 1932 I have covered the use of my alloy as an electrode for spark plugs and like devices. In this use its high resistance to corrosion insures long life, while its quality of ready emission of electrons reduces the voltage required to cause the spark to jump the gap.

The alloy here disclosed is especially valuable when used as an emitter in vacuum tubes and similar devices. Here resistance to corrosion is of slight importance, but the increased emission and reduced evaporation resulting from the action of chromium contributes very greatly to the emciency and life of the emitter. In this use the higher barium contents are preferred.

When a cathode made of the alloy is oxidized and activated in the manner described and claimed in the prior application of Ora S. Dufiendack and Ralph A. Wolfe, Serial No. 536,676, filed May 11, 1931, the emission is increased many times over.

It is obvious that this alloy will find application wherever one or more of the properties of high electronic emission, good heat and electrical conductivity and high resistance to heat and corrosion are needed. Other uses for the alloy will undoubtedly develop as knowledge of its properties becomes more widely known.

I claim:

1. An alloy consisting of nickel-cobalt metal, a measurable amount of barium and a measurable amount of chromium, with the nickel-cobalt metal constituting about 90% or more of the alloy.

2. An alloy characterized by high electron emissivity and resistance to heat and corrosion consisting of nickel-cobalt metal, a measurable amount of barium, and from a measurable amount to 10% chromium, with the nickel-cobalt metal constituting about 90% or more of the alloy.

3. An alloy containing approximately from .01% to .80% barium, from a measurable amount to 10% chromium, and the balance consisting principally of nickel.

4. An alloy consisting of from .01% to .80% barium, from a measurable amount to 10% chromium, and the balance consisting principally of nickel and a small proportion of a deoxidizer for imparting workability to the alloy.

5. An alloy consisting of from .01% to .80%

barium, .5% to 10% chromium, from a measurable amount to 2% manganese, and the balance nickel.

6. An alloy comprising from .01% to .80% barium, from .5% to 10% chromium, and from 87 to 99.5% nickel-cobalt metal, said barium, chromium and nickel-cobalt metal amounting to at least 98% of the alloy.

7. An alloy comprising from .01% to .80% barium, from .5% to 10% chromium, and from 87 to 99.5% nickel, said barium, chromium and nickel amounting to at least 98% of the alloy.

8. An alloy characterized by high electron emissivity and resistance to heat and corrosion containing a measurable amount of barium, from a measurable amount to 10% chromium, and the balance consisting principally of nickel.

9. In the manufacture of electron emitters of alloys of an alkaline earth metal and nickel, the method of inhibiting evaporation of the emitting material from the alloy and obtaining a stable emitting surface which consists in incorporating chromium in the alloy.

10. In the manufacture of electron emitters of nickel-barium alloys, the method of increasing electron emissivity which consists in incorporating chromium in the alloys in amounts not over 10%.

11. An alloy characterized by ready emission of electrons and stability of emitting surface comprising nickel as a major constituent and barium and chromium as minor constituents, said alloy being substantially free of iron.

12. An electron emitter made of an alloy consisting predominantly of nickel, chromium and an alkaline earth metal.

13. An electron emitter made of an alloy consisting predominantly of nickel, chromium and barium.

14. An electron emitter made of an alloy comprising nickel as a base metal, an alkaline earth metal to impart high electron emissivity to the alloy, and chromium to increase emissivity and retard evaporation of the emitting material.

15. An electron emitter made of an alloy comprising nickel as a base metal, a portion of barium to impart high electron emissivity to the alloy, and chromium to increase emissivity and retard evaporation of the emitting material.

DONALD W. RANDOLPH. 

